Effect of Transition Metal Compounds on Amorphous SiC Removal Rates

Abstract

We show here that transition metal compounds when used as additives to silica dispersions enhance a-SiC removal rates (RRs). Silica slurries containing KMnO 4 gave RRs as high as 2000 nm h −1 at pH 4. Addition of CuSO 4 to this slurry further enhanced the RRs to ∼3500 nm h −1 at pH 6. Furthermore, addition of a low concentration of 250 ppm Brij-35 to this slurry suppressed the RRs of SiO 2 to zero, while retaining the RRs of a-SiC at ∼2700 nm h −1 , a combination of RRs that is appropriate for hard mask polishing. The underlying mechanisms causing the enhancement in the RRs of a-SiC in the presence of transition metal compounds is discussed based on the RR data and XPS analysis of post-polished wafer surfaces. It is shown that a mixed redox system consisting of the oxidation of a-SiC by KMnO 4 enhanced by the catalytic activity of the Cu(II) salt is responsible for the rapid oxidation of a-SiC and the observed enhancement in polish rate with silica based slurries. The adsorption characteristics of Brij-35 on the oxide and carbide surfaces are described based on thermogravimetry data and in achieving the desired polish rate selectivity. Amorphous SiC (a-SiC) thin films, deposited at a low temperature of ∼400• C using a plasma enhanced chemical vapor deposition (PECVD) process, have excellent chemical and temperature resistance and a wide bandgap. These characteristics make them suitable as etch masking layers during advanced semiconductor, solar cell and micro-electro mechanical system (MEMS) fabrication.1-16 Examples of these applications include deep etching of glass or silicon, protection of low-K dielectric films, as a stop layer in STI CMP, etc. 10,12,14 The planar surface necessary to use a-SiC as a hard mask in these applications can be potentially achieved using chemical mechanical planarization (CMP).14 Since, the a-SiC hard mask layers typically protect an underlying dielectric material, generally SiO 2 , the CMP polish process must be selective to it. To the best of our knowledge slurries that can selectively polish SiC over SiO 2 have not been reported.Early work on developing slurries for 6H-SiC CMP showed that Cr 2 O 3 -based slurries increased the removal rates (RRs) compared to the traditional abrasives and oxidizers. 24 reported that slurries containing "soft functionalized particles" coated with several layers of "transition metal catalysts" yielded RRs ranging from 100 nm h −1 to 2500 nm h −1 depending on the concentration of the additives, the abrasives used and the operating conditions. The final surface quality was reported to be very good. In all these cases where high RRs were reported, 22,24 the effect of pressure and other operating conditions, the role of pH, the mechanism of the polish process and the role of various additives that are typically required for evaluating CMP processes were not discussed. More importantly, no slurries that lead to a selective removal of any type of SiC over * Electrochemical Society Active Member.z E-mail: babu@clarkson.edu SiO 2 that is needed for mask ...

Selective Polishing of Amorphous Silicon Carbonitride (a-SiCN) Films Over Silicon Dioxide and Silicon Nitride Films for Hardmask Applications

“…Comparison with a:SiC film polishing.-Several researchers reported results from polishing what were called a:SiC films, but in several cases these films also contained N atoms 8,9,33,34 and hence may be compared with our results. For example, Lagudu et al found that nitrogen was present in concentrations ranging between 4% and 7% near the surface of the a:SiC films used in their study.…”

“…Unlike in our work here, Lagudu et al used H 2 O 2 and KMnO 4 as oxidizers in silica slurries to enhance a:SiC RRs. 8,9 Addition of CuSO 4 to a silica slurry containing KMnO 4 further enhanced the RRs. 9 Based on the XPS analysis of post-polished surfaces, they proposed that MnO 4 − oxidizes the C atoms of a:SiC to alcohols and Cu 2+ ions catalyze the oxidation of alcohols to aldehydes or acids leading to the formation of polar bonds like Si-O, C-O, C=O, etc.…”

“…8,9 Addition of CuSO 4 to a silica slurry containing KMnO 4 further enhanced the RRs. 9 Based on the XPS analysis of post-polished surfaces, they proposed that MnO 4 − oxidizes the C atoms of a:SiC to alcohols and Cu 2+ ions catalyze the oxidation of alcohols to aldehydes or acids leading to the formation of polar bonds like Si-O, C-O, C=O, etc. that are easily polished off by silica abrasives resulting in high RRs.…”

“…2,3,7 While most of the previous studies focused on development of slurries for single crystal silicon carbide (SiC) or a: SiC and SiN films, our objective here is to formulate slurries for selective polishing of a-SiCN films over silicon dioxide and SiN films. [8][9][10][11][12] There are very few studies on CMP of a-SiCN films in published literature unlike CMP of SiC and SiN films. Bian developed slurries containing anionic surfactants to polish a-SiCN films but the RR values and other experimental details were not revealed.…”

PASSIVATION OXIDATION OF THE SURFACE OF AMA Al87Ni8Y5 IN THE PRESENCE OF OXYGEN-CONTAINING INHIBITORS

“…Відомий також спосіб покриття поверхні порівняно менш благородними металами, які легко піддаються окисненню, утворюючи на поверхні оксидні або гідроксидні захисні шари [6][7][8][9][10]. Однак такі самочинно утворені захисні шари бувають недостатньо однорідними, тому для їхнього ущільнення використовують збагачені на оксиген сполуки [11][12][13][14][15]. За теорією корозії [16] на поверхні сплаву утворюється захисний оксид легуючого елемента, який ускладнює дифузію та окиснення основного металу.…”